1. Technical Field
The invention concerns a piston having an oil duct for an internal combustion engine.
2. Related Art
Pistons for internal combustion engines are exposed to extremely high mechanical and thermal loads during operation so that it has to be ensured that the cylinder and piston portions that are exposed to constant friction due to their motion are sufficiently cooled and lubricated in order to keep friction as low as possible.
One measure is to provide in the piston an annular circumferential cooling channel in the region of the piston crown, for example, into which a cooling means, such as oil can be injected by means of at least one inlet opening. The supply of cooling oil is usually effected during the down stroke, while the piston moves toward an oil spray nozzle. The discharge of oil is usually performed by pressing the oil through inertial forces against the lower side of the cooling channel during the upstroke of the piston and pressing it out of the cooling channel.
The lubrification in the four-stroke engine is, for example, effected by means of a pump supplying the oil to the lubricating points. Such a lubricating point is inter alia present between the piston and the cylinder wall. Due to the motion of the piston, a certain amount of oil is wiped off the piston crown and may spread along the piston circumference to other regions of the piston, too. Here, the movable portions between the bolt opening/bolt and bolt/upper connecting rod eye need to be emphasized as lubrication is absolutely necessary in these regions but a direct supply of lubricating oil is difficult. The reason for this is that these regions are subject to a permanent up-and-down movement and are, thus, difficult to access.
In the prior art, the small connecting rod eye and also the bolt receive the oil through spray oil (oil mist) and/or through a bore in the shaft of the connecting rod. Oil leaking from the connecting rod bearings of the crank shaft is indirectly thrown by centrifugal force onto the cylinder walls and also the above-mentioned regions. The generation of an oil mist may be effected in various ways. For example, oil spray nozzles and/or lubrication pins may be provided in order to uniformly distribute the oil.
In the prior art, due to this indirect oil supply to the lubricating points around the bolt opening and around the upper (small) connecting rod eye it may happen that these regions can be supplied with splash oil only insufficiently and/or in an undefined manner.
JP 08 121 243 discloses a piston for an internal combustion engine having a protruding portion and a recessed portion in the region of the bolt opening. DE 10 2005 041 001 A1 discloses a light-weight piston in which a connection between an annular groove and the bolt opening is provided.
WO 2006/072293 A1 concerns a piston in which an oil conduit is provided toward a so-called window face at the lower side of the piston and, thus, toward an oil pan.